Method of Installing a Heat Tube on Pre-Insulated Piping

ABSTRACT

A method is shown for installing a heat tube on a section of pre-insulated piping. A metal carrier pipe is covered with a first layer of foam insulation. Next, a routing device is used to cut a longitudinal slot along the length of the pipe so that the pipe exterior surface is exposed from the insulation. A heat tube is then installed within the longitudinal slot, whereby the heat tube contacts the exterior surface of the metal carrier pipe. A second layer of foam insulation is then sprayed onto the exterior of the metal carrier pipe, covering the previously formed longitudinal slot and installed heat tube. A polyolefin coating is then applied over the insulation to form a protective outer jacket for the insulated pipe.

1. CROSS REFERENCE TO RELATED APPLICATIONS

The present case is a continuation-in-part of an earlier filedapplication Ser. No. 16/017,377, filed Jun. 25, 2018, by Thomas JosephKeyes, which, in turn, was a continuation-in-part of Ser. No.15/583,506, filed May 1, 2017, by Thomas Joseph Keyes, both entitled“Method of Installing a Heat Tube on Pre-Insulated Piping”.

2. FIELD OF THE INVENTION

The present invention relates generally to fully bonded foampre-insulated piping systems and, more specifically, to a method forinstalling a heat tube on such a pre-insulated pipeline.

3. DESCRIPTION OF THE PRIOR ART

Insulated pipelines are needed in a variety of situations. For example,distributed HVAC (heating, ventilation, and air conditioning)applications utilize chilled water for cooling and steam and hot waterfor heating. The chiller and boiler are typically contained in a centrallocation and the chilled water and steam and hot water are distributedto other locations. For example, on a school campus the chiller andboiler may be located in a power plant building. The chilled water andsteam are distributed to classrooms in separate buildings. A set ofinsulated pipelines is used to convey the chilled water from the chillerto other locations and back to the chiller. Another set of insultedpipelines is used to carry the steam or hot water from the boiler to theother locations and back to the boiler. It is necessary for the pipes tobe insulated in order to retain the internal temperature of the mediumbeing transported and keep heating and cooling losses at a minimum. Theinsulated pipelines are usually located underground.

So called “pre-insulated piping systems” of the type under considerationare conventional and commercially available. There are predominately twotypes of such pre-insulated piping systems in use: Class-A drainabledryable testable (DDT); and polyurethane or polyisocyanurate “fullybonded” foam systems. In the bonded type system, the foam and outerjacket, being bonded, do not move relative to the inner pipe. In theClass-A type system, on the other hand, the insulated inner pipe isdesigned to move independently of the associated outer jacket. In fact,there is an air gap between the inner pipe and outer carrier pipe in theclass-A type system.

The present application is directed toward the bonded foam type system.These systems utilize a metal carrier pipe, typically of steel, toconvey fluid, i.e., steam and/or superheated water, where the fluid isat a different temperature as compared to the ambient environment. Inthe particular types of piping systems under consideration, thepipelines may also be used to convey process fluids, heating water andhydrocarbon products, for example. In any event, around the outside ofthe steel pipe is a layer of insulating foam such as, for example, apolyurethane foam or a polyisocyanurate foam. In the case of hightemperature piping systems, the insulating foam serves to keep heat lossfrom the starting location of the pipeline to the ending location at aminimum. Around the outside of the foam is a thin jacket ofthermoplastic material, such as high density polyethylene (HDPE). Theplastic jacket protects the foam from mechanical damage and alsoprovides a watertight seal to prevent corrosion of the steel pipe.

In the typical pre-insulated piping manufacturing process, the steelcarrier pipe is typically rotated while a foam dispensing head passesdown the length of the pipe applying the foam coating. Alternatively, ahelical conveyor system may be used to rotate the pipe as it travelsdown the conveyor. In other known processes, an outer envelope is placedabout the length of the inner carrier pipe and foam is then injectedfrom one end into the annular area between the pipe exterior and theinterior of the outer envelope.

The above type processes have been used for many years and are adequatefor most types of pre-insulated piping systems. However, in some cases,it is desirable to install what is called a “heat tube” on the exteriorof the inner steel carrier pipe. Heat tubes are used, for example, as apart of “heat tracing” systems. Heat tracing is the use of an externallyapplied heat source on a pipeline to compensate for heat losses throughthe thermal insulation. Heat tracing evolved because of the need tomaintain the flow of low, medium and high temperature liquids through apipeline, whatever the nature of the surrounding environment. These typesystems are commonly used for temperature maintenance and freezeprotection and in heating/reheating applications in the transport ofprocess fluids, heating water and heavy petroleum products. The term“heat tube”, as used in the discussion which follows, is also intendedto cover other applications, such as where the tubes carry electricalwires or cables for other purposes than heat transfer. For purposes ofexplaining the method of the invention, however, an electric heattracing system will be utilized.

Various types of heat tracing systems exist. However, electric heattracing systems offer significant advantages. Generally speaking,electric beat tracing supplies only the heat necessary for the efficientflow of product through the pipeline, and only when required. Becauseelectric tracing is easily controllable, temperature variance isminimized and operating costs are significantly reduced. Time consumingcostly purging of the heat lines is also eliminated in many cases.

Whatever type of electric heat tracing system is, it is generallynecessary to install the previously described “heat tube” on theexterior surface of the metal carrier pipe. The heat tube is typically ametal or plastic conduit or channel member which is used to contain theelectrical cabling or wiring used in the system and to transfer heat tothe inner metal carrier pipe, as will be described more fully in thedescription which follows. The installation of the heat tube on theexterior surface of the inner metal carrier pipe presents somechallenges in the case of pre-insulated piping systems, however, due tothe presence of the outer foam insulating layer and the outer protectivejacket.

Thus, there continues to be a need for improvements in the pre-insulatedpiping manufacturing processes, particularly where a heat tube is to beinstalled for such purposes as an electric heat tracing system.

It is, therefore, an object of the present invention to provide a simpleand cost effective process for installing such a heat tube on theexterior surface of the inner metal carrier pipe as a part of apre-insulated piping system.

SUMMARY OF THE INVENTION

The present invention concerns a method for installing a heat tube on asection of pre-insulated piping. The pre-insulated piping is made up offirst and second lengths of insulated and jacketed pipe, each having ajoining end to be joined to an end of the other length. Each pipe lengthcomprises an inner metal carrier pipe having an interior surface and anexterior surface, an envelope of foamed insulation surrounding the innermetal carrier pipe exterior surface, and an outer protective jacketsurrounding the envelope of insulation. The joining ends of adjacentmetal carrier pipe lengths are welded together to form fixed joints,whereby the adjacent pipe lengths provide a continuous length of fluidconduit for conveying fluids.

The preferred method of the invention comprises the steps of:

providing a steel carrier pipe having an exterior surface, an interiorsurface and a given length extending along a central longitudinal axis,the steel carrier pipe having a first layer of foam which has previouslybeen sprayed onto the exterior surface thereof, the foam covered pipehaving also been cured at a curing station to allow the sprayed foam tocure to a given radial thickness to thereby form a foam insulated pipe;placing the foam insulated pipe on a conveyor and moving the foaminsulated pipe down the conveyor to a cutting station which includes acutter assembly;providing a carriage assembly located at the cutting station which isassociated with the cutter assembly and moving the carriage assembly onas associated track linearly down the exterior of the foam insulatedpipe, whereby the cutter assembly cuts a longitudinal slot through thefirst layer of foam insulation along at least a portion of the length ofthe steel carrier pipe, thereby exposing the exterior surface of thesteel carrier pipe;installing a heat tube within the longitudinal slot whereby the heattube contacts the exposed exterior surface of the metal carrier pipe;passing the pipe past a second foam application station while spraying asecond layer of foam insulation onto the exterior of the metal carrierpipe, thereby covering the previously formed longitudinal slot andinstalled heat tube;applying a synthetic polymeric coating around the insulated pipe tothereby form an outer protective jacket for the insulated pipe.

The cutter assembly can assume various forms, but can convenientlycomprise a wire brush or a blade, or other device capable of cutting orforming a longitudinal channel in the first layer of foam insulationwhich is applied onto the exterior surface of the metal carrier pipe.

The lengths of insulated piping being joined can be used, for example,as a part of a pipeline conveying process fluids, heating water orpetroleum products. The insulated pipes can be used as a part of anelectric current tracing system which is used for temperaturemaintenance and freeze protection.

The preferred insulating foams are selected from the group consisting ofpolyurethane foams and polyisocyanurate foams. The carrier pipe beinginsulated is a metal pipe which is preferably formed of steel of a givengauge. One preferred material for the outer protective jacket is a highdensity polyethylene jacket material.

The process for installing a heat tube on the exterior surface of theinner metal carrier pipe can be performed in a batch manufacturingoperation, or in a continuous or semi-continuous operation, as will bedescribed more fully in the written description which follows.

Additional objects, features and advantages will be apparent in thewritten description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified representation of a typical prior artpro-insulated electric heat traced steel piping installation.

FIG. 2 is a simplified, schematic view of the first step in themanufacturing process of the invention in which an inner metal carrierpipe is coated with a layer of foam insulation.

FIG. 3 is a simplified view, similar to FIG. 2, showing the next step inthe process in which a wire electric brush is used to cut a longitudinalslot in the previously applied layer of foam insulation.

FIG. 3A is a simplified, isolated view of a blade fixture which can alsobe used as the routing device in the process of the invention.

FIG. 4 is a view of the next step in the process of the invention inwhich a steel heat tube is installed in the previously cut slot.

FIG. 5 is illustrates the next step in the process in which anadditional layer of foam insulation is applied to the partly insulatedpipe, covering the steel heat tube and longitudinal slot.

FIG. 6 is illustrates the final step in the process of the invention inwhich an outer protective synthetic jacket is applied about the exteriorof the previously insulated pipe and steel heat tube.

FIGS. 7A and 7B are simplified, partly schematic views of a continuousmanufacturing process for installing a heat tube on pre-insulated pipingin which a cutting device is mounted in a suitable fixture and the foaminsulated carrier pipe is moved past the fixture in linear fashion toform a longitudinal slot in the first layer of foam on the foaminsulated carrier pipe.

FIGS. 8A to 8C are simplified, partly schematic views of another versionof a continuous manufacturing process in which the cutter assembly ismoved down a stationary foam insulated pipe to cut a longitudinal slotin the foam.

FIG. 9 is an isolated view of the carriage assembly which is used topull the cutter assembly down a longitudinal track using rack and piniongear assemblies.

FIG. 10A is an isolated view of one of the side cutting blades used inthe cutter assembly of the invention.

FIG. 10B is a perspective view of the cutting blade of FIG. 10A.

FIG. 10C is an isolated, perspective view of the entire cutter assembly.

FIG. 10D is a front end view of the cutter assembly of FIG. 10C.

FIG. 10E is a side view of the cutter assembly of FIG. 10C.

DETAILED DESCRIPTION OF THE INVENTION

The preferred version of the invention presented in the followingwritten description and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingexamples included in the accompanying drawings and as detailed in thedescription which follows. Descriptions of well-known components andprocesses and manufacturing techniques are omitted so as to notunnecessarily obscure the principle features of the invention asdescribed herein. The examples used in the description which follows areintended merely to facilitate an understanding of ways in which theinvention may be practiced and to further enable those skilled in theart to practice the invention. Accordingly, the examples should not beconstrued as limiting the scope of the claimed invention.

As has been briefly described, the particular type of piping systemunder consideration includes lengths of insulated and jacketedpre-insulated piping and, more specifically to a bonded foampre-insulated piping system; i.e., the piping is made up of an innercarrier pipe having an interior surface and an exterior surface with anenvelope of foamed insulation surrounding the inner pipe exteriorsurface. The envelope of foamed insulation can be, for example, aninsulating material selected from the group consisting of polyurethanefoams and high temperature polyisocyanurate foams. An outer protectivejacket surrounds the envelope of insulation. The outer jacket canconveniently be formed from a polyolefin, such as a high densitypolyethylene. Each length of piping has a joining end for joining to anadjacent length of piping, whereby the adjacent lengths of pipingprovide a continuous length of fluid conduit for conveying hightemperature fluids. The section of piping, as previously described, isinstalled in a piping system made up of other sections of piping.

One example of a commercially available pre-insulated piping system ofthe above type is the “HT-406” ™ High Temp Steel Piping System sold byThermacor Process, Inc., 1670 Hicks Field Road East, Fort Worth, Tex.76179. The following references, among others, teach the manufacture ofsuch prior art systems: U.S. Pat. Nos. 3,793,411; 4,084,842; and U.S.Pat. No. 4,221,405, all to Stonitsch et al.; as well as U.S. Pat. No.6,547,908; U.S. Pat. No. 5,736,715; U.S. Pat. Nos. 7,037,557; 7,418,979;and 9,377,150, all assigned to Thermacor Process, Inc., the assignee ofthe present invention.

Any reference in this discussion to “sections” or “lengths” of pipe isintended to refer to standard available factory pre-insulated piping ofthe type previously described having an inner metal pipe surrounded byan envelope of foamed insulation, which in turn, is contained within apolyolefin jacket. As referred to briefly above, typical commercialpractice involves the use of steel, copper, aluminum or alloy metalmaterial for the inner carrier pipes. The typical pipe diameters willbe, for example, 4 inches to 12 inches. The insulating foam may be, forexample, a suitable polyurethane foam. For high temperature systems, thesurrounding envelope of foam insulation is typically formed of closedcell polyisocyanurate. The outer protective jacket in such systems canbe formed of a suitable polyolefin, such as polypropylene, polybutylene,polyethylene, polyvinylchloride and similar protective jackets.

The term “high temperature”, as used in this discussion, means that thepipelines are conveying fluids at temperatures above ambient, typicallyat temperatures of 212° F. and above. In some cases, temperatures of350°−400° F. and higher will be encountered. The expected operatingtemperature of the pipeline will determine the type of outer foaminsulation utilized. For example, 250° F. is generally accepted as thepresent temperature limitation at which polyurethane foam is used inbonded foam systems. Temperatures above about 250° F. generally requirethe use of higher temperature foams, such as the previously mentionedpolyisocyanurate foam. For example, a typical steam line might beconveying fluid at, for example, 250-350° F. In the case of the “heattracing” systems of the type to be described, the piping system may beused, for example, as a part of a pipeline conveying process fluids,heating water or petroleum products. In such cases, the fluid beingconveyed may be at a lower temperature, so that a polyurethane foaminsulation is sufficient.

Several types of electric heat tracing methods are available, dependingupon the end application. For example, one type is known as “skin effecttracing.” Electric skin effect current tracing can be thought of ascombining the engineering principles of “skin effect” and “proximityeffect.”

Skin effect is an alternating current phenomena whereby AC current flowsin the outer surface of a steel conductor. Proximity effect is anelectromagnetic force which operates based upon the fact that equalcurrents in opposite directions attract. By placing the electric cableinside the heat tube, the current is drawn to a thin section of the heattube inner wall. Heat generated from the current passes through the heattube wall and into the steel carrier pipe by conduction. Exteriorsurfaces of skin effect current systems are electrically grounded. Thevoltage is impressed between the cable and the inner surface of the heattube.

Skin effect heating allows a single point connection to provide heat fordistances as long as 15 miles and even greater. Since electricity onlyflows on the inside of the heat tube, any residual voltage iseliminated. Since skin effect heating allows the heat applied to beevenly dissipated over long distances, an even temperature profile canbe achieved.

One skin effect heating system is sold by Thermacor Process, Inc., FortWorth, Tex., as the Ferro-Therm HDPE Skin Effect Heating System™.Exemplary Specifications, somewhat simplified for ease of explanation,include the following:

A. Carrier Pipe shall be steel ASTM A-53, Grade B, ERW (Type e) orseamless (Type S), standard weight Piping shall generally be provided in40 foot double random lengths where feasible. Straight sections offactory insulated piping shall have 6″ of exposed pipe at each end forfield joint fabrication.B. A steel heat tube (cylindrical conduit) of A106, Seamless Sch. 40pipe will be installed along the entire length of the carrier pipe. Thiscould also be a channel member to accomplish the same purpose.C. An electric skin effect heat trace system will be custom designed forthe specific application and installation conditions.D. Polyurethane foam insulation shall be used to cover the carrier pipein the annular space between the carrier pipe and the ultimate outerHDPE jacket with a minimum thickness of one inch. Insulation shall berigid 90-95% closed cell polyurethane with a 2.0-3.0 pounds per cubicfoot density and coefficient of thermal conductivity 9K-factor) of 0.14and shall conform to ASTM C-591.E. The outer jacketing material shall be extruded black, high densitypolyethylene (HDPE) manufactured in accordance with ASTM D-1248 having aminimum wall thickness of 150 mils.

The above specification extracts are intended to be exemplary only asthe specifications may vary to some extent, depending upon the endapplication for the heat trace system. These specifications are intendedto provide some understanding of the basic types of materials used in atypical system of the type under consideration.

Turning now to FIG. 1, there is shown in somewhat simplified fashion aheat tracing system, which in this case happens to be an “electric skineffect heat trace system.” There are typically six main components inmost skin effect systems. A control panel 11 is used to monitor theprocess temperature and to adjust the power input. A transformer 13 isused to regulate the voltage applied to the system. Various temperaturesensors 15 are used to monitor the process temperatures. Skin effectelectrical wires or cabling 17 are used to carry the voltage over thelength of the pipeline system. Tubing or channeling 19 providesprotection for the electrical wires and dissipates the heat energy tothe pipeline. Junction boxes, such as pull box 21 and end terminationbox 23 are used for wire connection and wire pulling points.

This somewhat schematic illustration of a typical skin effect heattracing system is intended to be exemplary only of one type of heattraced piping system. However, for whatever type heat traced systemhappens to be under consideration, there is generally the need toprovide a “heat tube” to house the various electrical wires or cablingused in the system. FIGS. 2-6 which follow illustrate the improvedmethod of the invention which is used to install such a heat tube on asection of pre-insulated piping.

Turning to FIG. 2, there is shown, in simplified fashion, the first stepin one version of the manufacturing process of the invention. The methodis used for installing a heat tube on a section of pre-insulated pipingwhere the piping is made up of first and second lengths of insulated andjacketed pipe, each having a joining end to be joined to an end of theother length. Each pipe length comprises an inner metal carrier pipehaving an interior surface and an exterior surface. An envelope offoamed insulation surrounds the inner metal carrier pipe exteriorsurface, and an outer protective jacket surrounds the envelope ofinsulation. The joining ends of adjacent metal carrier pipe lengths areeventually welded together to form fixed joints, whereby the adjacentpipe lengths provide a continuous length of fluid conduit for conveyingfluids, as has been described.

In the first step of the method illustrated in FIG. 2, a section ofsteel carrier pipe 25 has an exterior surface 27, an interior surface 29and a given length (‘T’ in FIG. 3) extending along a centrallongitudinal axis 31. The carrier pipe is placed on a helical conveyorsystem which rotates the pipe as it translates down the conveyor. Afixed foam dispensing head 35 sprays a layer of insulating foam 38 onthe carrier pipe as it passes through the spray head path. As has beendiscussed, this might be a polyurethane foam sprayed to a depth of, forexample, one inch thick. This part of the process is conventional andwill be familiar to those skilled in the relevant arts.

The first layer of insulating foam will generally be sprayed to a depthwhich corresponds approximately with the height of the heat tube to beinstalled later. The layer of foam insulation is allowed to cure to agiven radial thickness to thereby form a foam insulated pipe. It may benecessary to utilize more than one dispensing head 35, for example, onehead above the pipe and one head below the pipe for evenly injectingfoaming material as the heads move down the length of the rotating pipe.

In the next step in the method, shown in FIG. 3, a routing device isused to cut a longitudinal channel or opening down a selected length ofthe foam covered pipe. For example, a wire brush 37 can be mounted in asuitable jig fixture 39 on the side of the foam insulated pipe 25. Inone version of the method of the invention, the pipe 25 is drawn pastthe wire brush 37 in a linear direction of travel to thereby cut alongitudinal slot 41 through the first layer of foam insulation at onepoint on the circumference of the steel carrier pipe, thereby exposingthe exterior surface 27 of the steel carrier pipe 25. The slot may be,for example, about one inch by one inch in dimension. The wire brush canbe something as simple as a typical wire wheel brush mounted on anelectric drill body. Suitable wire wheels and drill bodies are availableat Home Depot®, Lowes® and similar stores.

The routing device could also assume other forms, for example, FIG. 3Ashows a simple stationary blade 34 mounted in a suitable fixture 36. Asthe foam covered pipe passes longitudinally past the routing station,the blade cuts a longitudinal slot such as the slot 41 shown in FIG. 3.

FIG. 4 illustrates the next step in the method in which a metal orplastic heat tube 43 is installed within the longitudinal slot 41,whereby the heat tube 43 contacts the exposed exterior surface 27 of themetal carrier pipe 25. The heat tube 43 may be temporarily affixed tothe pipe exterior surface in some manner, but it is typically notnecessary to weld the heat tube in place. The heat tube 43 is shown asbeing a cylindrical conduit in the drawings, but it will be understoodthat the heat tube could have other shapes, such as a square orrectangular channel member, for example.

FIG. 5 illustrates the next step in the method in which a second layerof foam insulation 42 is sprayed onto the exterior of the metal carrierpipe and first layer of foam insulation 38, thereby covering thepreviously formed longitudinal slot 41 and installed heat tube 43.

In the final step in the process, shown in FIG. 6, an outer protectivesynthetic jacket 45 is applied to the carrier pipe and two layers offoam insulation. This can be accomplished, as by applying a polyolefincoating (HDPE) around the insulated pipe to thereby form an outerprotective jacket for the insulated pipe. In the example illustrated inFIG. 6, an extruder head 47 extrudes the HDPE coating from an extrusionnozzle 49 as the extrusion head passes longitudinally along the exteriorof the pipe. Alternatively, the extruder head can be stationary with thepipe being placed on a helical conveyor system which rotates the pipe asit translates down the conveyor.

The steps in the method which have previously been described could applyto a batch, stepwise process, or to a continuous or semi-continuousprocess. FIGS. 7A and 7B illustrate one embodiment of such a continuousprocess.

With reference to FIG. 7A, a steel pipe 51 rolls off onto a conveyorline 53 and moves from right to left, as viewed in the top portion ofFIG. 7A. The pipe is being translated in a longitudinal direction andalso simultaneously rotated as it travels down the conveyor line. Aftertraveling down a given length of the conveyor line 53, the pipe passes afoam application station 55 where a dispensing head 57 sprays a firstlayer of insulating foam onto the steel pipe. The foam may be sprayed,for example, to a depth of about 1.5 inches to match the general heightof the heat tube to be installed.

With reference to the top portion of FIG. 7B, the pipe then enters thecuring oven section 59 of the conveyor line and continues to move to theleft as viewed in the top portion of FIG. 78. At the far left end of thedrawing, the pipe is rolled off onto the second, straight line sectionof a conveyor line 61. The now foam covered pipe 63 moves from left toright, as viewed in the mid-section of FIG. 7B and continues over to arouting station (shown as 65 in FIG. 7A). In this version of the methodof the invention, the previously described wire brush or blade routingprocesses are then used to cut a longitudinal channel down the length ofthe foam covered pipe 63, as described with respect to FIGS. 3 and 3A.

The foam covered pipe 63, having the routed longitudinal channel orgroove previously described, then rolls off the end section 67 of thestraight line conveyor onto a work station (designated as 69 in FIG.7A). The previously described length of heat tube is then installed, inthis case by hand, into the longitudinal channel cut in each length ofpipe 71.

The lengths of pipe 71 then pass to another conveyor section 77 whichboth translates the lengths of pipe longitudinally and alsosimultaneously rotates the lengths of pipe. The lengths of pipe 71,having the installed heat tubes, are then moved from right to left, asviewed in the bottom portion of FIG. 7A, where they pass a second foamapplication station 73 where a dispending head 75 sprays a second layerof foam to cover the heat tube and open channel. The thickness of thesecond application of foam is determined by the required processspecification thickness.

The lengths of pipe 71 then pass through an application station (79 inFIG. 7B) where they are sprayed by dispensers 81, 83, with a vaporbarrier and wrapped with the polyethylene outer jacket previouslydescribed. The finished pipe lengths 85 then pass from right to left, asviewed in the bottom portion of FIG. 7B and roll off to a finishing area87. The process line used in the continuous, or semi-continuous processdescribed can easily run on the order of fifteen feet per minute.

FIGS. 8A to 10E illustrate another embodiment of the present inventionin which the foam insulated pipe is stationary and a cutter assemblymoves down the longitudinal axis of the carrier pipe in linear fashionto cut a longitudinal slot in the foam. Turning first to FIG. 8A, thereis shown a supply 89 of previously manufactured foam insulated metalcarrier pipes located adjacent a conveyor 91. The previouslymanufactured foam insulated pipe 89 could have been manufactured aspreviously described with reference to FIGS. 7A and 7B of the Drawings.In other words, these sections of pipe already have a first layer offoam insulation applied on their exterior surfaces but do not yet have alongitudinal channel. In FIG. 8A, one stand of pipe 93 has been fed ontothe conveyor section 91.

With reference now to FIG. 8B, there is shown a top view of the nextsection of conveyor, designated generally as 95. This section ofconveyor would receive the stand of pipe 93 from FIG. 8A and would movethe pipe in linear fashion, from left to right as viewed in FIG. 8B andinto position with one end of the pipe adjacent the cutter assembly 99.The stand of pipe 93 is not shown in FIG. 8B so that it does notobstruct the view of the conveyor section 95 and other operative partsof the assembly.

Once the section of pipe 93 abuts the leading edge 101 of the cutterassembly 99, any linear movement of the pipe section stops so that thepipe section is now held in stationary fashion. The cutter assembly 99is now moved down the longitudinal axis of the stationary pipe sectionto cut one or more longitudinal slots in the foam which is located onthe exterior surface of the carrier pipe. This is to be contrasted withthe method of the invention shown in FIGS. 7A and 7B in which the pipemoved relative to the stationary routing station. The pipe section 93,with at least one longitudinal slot 103, is now fed linearly onto theconveyor section 105 and subsequently rolled off onto the storage area107.

The above discussion describes the method used to cut a longitudinalslot in a previously insulated pipe. The pipe would then be furtherprocessed to apply the second layer of foam insulation and outerpolyolefin jacket as has been described with respect to FIGS. 5 and 6.

FIGS. 9 to 10E show further details of the carriage assembly 97 andcutter assembly 99 used in the method of the invention. FIG. 9 is anisolated view of the carriage assembly 97 on its associated track withthe cutter assembly removed for ease of illustration. The carriageassembly 97 can be provided with cam followers, such as rollers 109,111,113 shown in FIG. 9 which are mounted on associated rails, such asrails 115, 117 provided as a part of the track. Any of a number ofsuitable means can be utilized for moving the carriage assembly down therails 115, 117 in linear fashion. For example, a simple rack and pinionmechanism (illustrated schematically as 119 in FIG. 8B) could beutilized. The cam followers eliminate tension and rotation of thecarriage with respect to the associated track.

The carriage assembly is used to push and pull the cutter assembly 99down the track formed by the associated rails 115, 117. In other words,the carriage assembly moves the cutter assembly down the exteriorsurface of the previously insulated metal carrier pipe to cut thelongitudinal channel which will ultimately house the heat tube. The pipeis then moved further down the conveyor line and the carriage assemblyand cutter assembly are retracted back to the original, startingpositions in preparation for receiving a subsequent section of foaminsulated pipe.

FIG. 10C is an isolated, perspective view of the cutter assembly 99. Thecutter assembly has a generally arcuate body portion 121 which housesone or more cutter blade assemblies, such as the assemblies 123, 125,127, shown in FIG. 10C. The assemblies 123, 125, 127 are generallyequidistantly spaced about the arcuate body portion, extending outwardlyalong a longitudinal axis which is parallel to the longitudinal axis ofthe foam coated pipe. While the cutter assembly 99 shown in FIG. 10Cuses three cutting blade assemblies, there could be other arrangements,such as the provision of only two, equidistantly spaced cutter bladeassemblies. The top skin 129 of the cutter assembly 99 is designed tominimize blockage of the foam channel being formed.

Two identical runner assemblies 131, 133, connect to the carriageassembly 97 at two points by a cable (not shown) to maintain consistentpulling on the pipe exterior surface. The arcuate body of the cutterassembly 99 has lower side rails 135, 137 which house associatedrollers, such as rollers 139 shown in FIG. 10C. The rollers allow thecutter assembly to ride on the conveyor and associated track shown inFIG. 9. The conveyor is not shown in FIG. 9, for ease of illustration ofthe carriage assembly and track, but can be seen as 95 in FIG. 8B. Asshown in FIGS. 10D and 10B, each of the cutter blade assemblies, hashard plastic runners 141, 143, 145 which track on the pipe exteriorsurface during the cutting operation.

As can be seen in FIGS. 10A and 10B, each of the cutter blade assemblieshas a hardened front cutting blade 147 which is preferably adjustableand replaceable and side cutting blades 149 which are also preferablyadjustable and replaceable. There are also hard plastic runners, such asrunner 151 located at the rear of each of the cutter blade assemblieswhich can be replaceable. The cutter blade assemblies can also beprovided with compressed air ports (153 in FIG. 10B) for helping toclear the cut foam. They can also be provided with a recessed area 155for receiving an optional abrasive brush which would be used to cleanthe metal exterior surface of the carrier pipe as the outer foam layeris being cut away.

In operation, a section of previously foam coated metal carrier pipe (93in FIG. 8A) is moved down the conveyor sections 91 and 95 until the pipeleading end contacts the approximate location of the carriage and cutterassemblies (97, 99 in FIG. 8B) at a cutting station. The cutter assembly99 is then pulled down the track from the right to the left, as shown inFIG. 8B. This action causes the cutter blade assemblies 123, 125, 127,to cut three longitudinal channels in the first layer of foam whichcoats the exterior of the metal carrier pipe. The section of pipe thenmoves further down the conveyor section 95 to last section of conveyor(105 in FIG. 8C) where it is then off-loaded to an adjacent area 107. Inthe meantime, the carriage and cutter assemblies 97, 99, are pulled fromthe left to the right, as viewed in FIG. 8B and returned to theiroriginal positions at the cutting station. A subsequent stand of foaminsulated pipe is then moved down the conveyor section 95 to theapproximate location of the carriage and cutter assemblies at thecutting station, as they are shown in FIG. 8B, and the process isrepeated. The section of pipe with its longitudinal channels can then beprocessed as previously described with respect to FIGS. 5 and 6 to applya second layer of foam insulation (FIG. 5) and then an outer protectivelayer of HDPE (FIG. 6).

An invention has been provided with several advantages. The method ofthe invention can be used to manufacture a length of pre-insulatedpiping where the lengths of insulated piping being joined are part of apipeline conveying, for example, process fluids, heating water orpetroleum products. The process accommodates the installation of one ormore heat tubes of the type used in a heat tracing system used fortemperature maintenance and freeze protection. The process is relativelysimple in nature and economical to practice. The process can be easilyintegrated into existing pre-insulated foam pipe manufacturingprocesses.

While the invention has been shown in only one of its forms, it is notthus limited but is susceptible to various change and modificationswithout departing from the spirit thereof.

What is claimed is:
 1. A method for installing a heat tube on a sectionof pre-insulated piping where the piping is made up of first and secondlengths of insulated and jacketed pipe, each having a joining end to bejoined to an end of the other length, each pipe length comprising aninner metal carrier pipe having an interior surface and an exteriorsurface, an envelope of foamed insulation surrounding the inner metalcarrier pipe exterior surface, and an outer protective jacketsurrounding the envelope of insulation, the joining ends of adjacentmetal carrier pipe lengths being welded together to form fixed joints,whereby the adjacent pipe lengths provide a continuous length of fluidconduit for conveying fluids, the method comprising the steps of:providing a steel carrier pipe having an exterior surface, an interiorsurface and a given length extending along a central longitudinal axis,the steel carrier pipe having a first layer of foam which has previouslybeen sprayed onto the exterior surface thereof, the foam covered pipehaving also been cured at a curing station to allow the sprayed foam tocure to a given radial thickness to thereby form a foam insulated pipe;placing the foam insulated pipe on a conveyor and moving the foaminsulated pipe down the conveyor to a cutting station which includes acutter assembly; providing a carriage assembly located at the cuttingstation which is associated with the cutter assembly and moving thecarriage assembly on as associated track linearly down the exterior ofthe foam insulated pipe, whereby the cutter assembly cuts a longitudinalslot through the first layer of foam insulation along at least a portionof the length of the steel carrier pipe, thereby exposing the exteriorsurface of the steel carrier pipe; installing a heat tube within thelongitudinal slot whereby the heat tube contacts the exposed exteriorsurface of the metal carrier pipe; passing the pipe past a second foamapplication station while spraying a second layer of foam insulationonto the exterior of the metal carrier pipe, thereby covering thepreviously formed longitudinal slot and installed heat tube; applying apolyolefin coating around the insulated pipe to thereby form an outerprotective jacket for the insulated pipe.
 2. The method of claim 1,wherein the routing device includes at least one blade.
 3. The method ofclaim 2, wherein the foam insulation is selected from the groupconsisting of polyurethane foams and polyisocyanurate foam.
 4. Themethod of claim 3, wherein the lengths of insulated piping being joinedare part of a pipeline conveying process fluids, heating water andpetroleum products.
 5. The method of claim 4, wherein the outerprotective jacket is a high density polyethylene jacket material.
 6. Themethod of claim 5, wherein the outer protective jacket is spirallywrapped about the previously insulated pipe.
 7. A method for installinga heat tube on a section of pre-insulated piping where the piping ismade up of first and second lengths of insulated and jacketed pipe, eachhaving a joining end to be joined to an end of the other length, eachpipe length comprising an inner metal carrier pipe having an interiorsurface and an exterior surface, an envelope of foamed insulationsurrounding the inner metal carrier pipe exterior surface, and an outerprotective jacket surrounding the envelope of insulation, the joiningends of adjacent metal carrier pipe lengths being welded together toform fixed joints, whereby the adjacent pipe lengths provide acontinuous length of fluid conduit for conveying fluids, the methodcomprising the steps of: providing a steel carrier pipe having anexterior surface, an interior surface and a given length extending alonga central longitudinal axis; placing the carrier pipe on a conveyorwhich rotates the steel carrier pipe while simultaneously moving thepipe in a longitudinal direction past a first foam application stationwhere a first layer of foam insulation is sprayed onto the exteriorsurface of the metal carrier pipe; passing the foam covered pipe througha curing station located on the conveyor line and allowing the foaminsulation to cure to a given radial thickness to thereby form a foaminsulated pipe as it is being moved longitudinally down the conveyorline; passing the foam covered pipe to another section of straight lineconveyor where it continues to be moved in a longitudinal direction to acutting station which includes a cutter assembly; providing a carriageassembly located at the cutting station which is associated with thecutter assembly and moving the carriage assembly on an associated tracklinearly down the exterior of the foam insulated pipe from a startingposition to an ending position, whereby the cutter assembly cuts alongitudinal slot through the first layer of foam insulation along atleast a portion of the length of the steel carrier pipe, therebyexposing the exterior surface of the steel carrier pipe; installing aheat tube within the longitudinal slot whereby the heat tube contactsthe exposed exterior surface of the metal carrier pipe; moving the pipeto another section of conveyor which moves the pipe in a longitudinaldirection while simultaneously rotating the pipe; passing the pipe pasta second foam application station while spraying a second layer of foaminsulation onto the exterior of the metal carrier pipe, thereby coveringthe previously formed longitudinal slot and installed heat tube;continuing to move the pipe down a final section of conveyor whileapplying a polyolefin coating around the insulated pipe to thereby forman outer protective jacket for the insulated pipe; rolling the pipe offthe final section of conveyor into a finished pipe area.
 8. The methodof claim 7, wherein the cutter assembly includes at least one cuttingblade.
 9. The method of claim 8, wherein the foam insulation is selectedfrom the group consisting of polyurethane foams and polyisocyanuratefoam.
 10. The method of claim 9, wherein the lengths of insulated pipingbeing joined are part of a pipeline conveying process fluids, heatingwater and petroleum products.
 11. The method of claim 10, wherein theouter protective jacket is a high density polyethylene jacket material.12. The method of claim 11, wherein the outer protective jacket isspirally wrapped about the previously insulated pipe.
 13. The method ofclaim 7, wherein the foam insulated pipe is held stationary at thecutting station while the carriage assembly and cutter assembly move ina linear direction down a longitudinal axis of the pipe to form thelongitudinal slot on the exterior surface of the foam insulated pipe.14. The method of claim 7, further comprising the steps of: moving thefoam insulated pipe having the longitudinal slot further down theconveyor after the longitudinal slot is formed, followed by retractingthe carriage assembly and cutter assembly back along the associatedtrack to the starting position; and moving another section of foaminsulated pipe into position on the conveyor at the cutting station. 15.The method of claim 7, wherein the cutter assembly has a generallyarcuate body which houses one or more cutter blade assemblies, the bladeassemblies being generally equidistantly spaced about the arcuate bodyportion, extending outwardly along a longitudinal axis which is parallelto the longitudinal axis of the foam coated pipe.
 16. The method ofclaim 15, wherein at least two runner assemblies connect to the carriageassembly at two points by a cable, to thereby maintain consistentpulling force on the cutter assembly.
 17. The method of claim 16,wherein each of the cutter blade assemblies has a hardened front cuttingblade which is adjustable and replaceable and a pair of side cuttingblades which are also adjustable and replaceable.
 18. The method ofclaim 17, wherein hard plastic runners are located at the rear of eachof the cutter blade assemblies.